A polarizing plate has been generally used as a structure where a protection film is laminated on one surface or both surfaces of a polarizer formed of a polyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin dyed with a dichromatic dye or iodine by using an adhesive. In the related art, a triacetyl cellulose (TAC)-based film has been mainly used as the protection film for the polarizing plate, but there is a problem in that the TAC film is easily deformed under the high temperature and high humidity environment. Accordingly, recently, protection films of various materials which can replace the TAC film have been developed, and for example, a method where polyethylene terephthalate (PET), cycloolefin polymer (COP), and acryl-based films, and the like are used alone or are used while being mixed is proposed.
Among them, since the polyethylene terephthalate film has lower costs and excellent durability as compared to the other polymer films, in order to reduce manufacturing costs of the polarizing plate, attempts for using the polyethylene terephthalate film as the protection film for the polarizer have continued. However, in the case of the polarizing plate proposed until now, in which the polyethylene terephthalate film is equipped, there is a problem in that since an in-plane retardation value of the polyethylene terephthalate film is large, when the polyethylene terephthalate film is equipped in a display device, stripes or hazes by optical interference occur, and thus the visual sense is not good.
Further, in the case where the polyethylene terephthalate film is attached to one surface of the polarizer and a polymer film made of the other material, for example, the polymer film such as a triacetyl cellulose film, an acryl film, and a cycloolefin polymer film is attached to the other surface, there is a problem in that orthogonal optical properties of the polarizing plate, such as orthogonal luminance or the degree of polarization, are severely degraded. The aforementioned problem tends to be further intensified under a high-speed lamination process condition in which a lamination process is performed at a high speed in order to improve productivity.
Further, in the case of the polyethylene terephthalate film, there are problems in that since adhesion force with a polyvinyl alcohol-based adhesive used for adhesion of the polarizer and the protection film in the related art is low, after the polarizing plate is manufactured, stripping and lifting of the protection film and the like easily occur to reduce durability, and since moisture permeability is low, drying is not easy when a water-based adhesive is used.
Therefore, there is a demand for developing a polarizing plate where the polyethylene terephthalate film is used as the protection film, the polarizing plate manufacturing materials and processes in the related art, such as the water-based adhesive and the high-speed lamination process, may be used as they are, and an excellent optical property is secured.